A. Field of the Invention
The present invention relates generally to a method of improving the strength of briquettes made from lime based products, such as those made from dolomitic quicklime, through the use of a binder having a carbon constituent.
B. Description of the Prior Art
Lime based compounds have many practical uses in a variety of different industries. For instance, these substances are used in the steel industry, e.g., as fluxing agents; in treating waste water and sewage; as soil neutralizing agents and nutrients; in ground stabilization for construction; and as components for building materials.
A number of different chemical species are often lumped together under the generic term “lime.” For example, limestone is a mineral which is mined commercially and is used in various industries in crushed or powdered form. “Limestone” generally means CaCO3, while “dolomitic limestone” generally refers to the presence of MgCO3 or to a mixture of MgCO2·CaCO3. Powdered limestone is converted to quicklime, by a calcining operation, typically by roasting in rotary kilns. Quicklime may be high calcium, magnesian, or dolomitic and of varying degrees of chemical purity. Quicklime is slaked with water to form hydrated lime.
Thus, calcium oxide (CaO) is generally referred to in the industry as “quicklime”, while Ca(OH)2 is referred to as hydrated lime or “hydrate”, both types of materials often being referred to generically or informally as “lime”. Dolomitic quicklime has the formula CaO·MgO. Quicklime is usually provided in the form of lumps or pebbles. Dry hydrated lime is usually a powder. In order to further process these compounds and improve the ease with which they are handled, dry CaO,CaO·MgO or Ca(OH)2 can be mixed with water to form a slurry in a slaking operation. During the slaking of quicklime, large amounts of heat are generated which can significantly raise the temperature of the slurry.
Historically, the lime industry has maintained a material balance between lump or pebble quicklime and the fine quicklime generated during calcination and subsequent material handling. In regards to high calcium quicklime, the lime industry has developed markets for the fine quicklime, i.e., particles which are typically less than ¼ inch in size. In some situations, however, an excess of the fine quicklime is produced. As a result, there have been attempts in the industry to lump or agglomerate these fines together in the form of “briquettes”. The briquettes so produced not only eliminate excess fines but also increase the amount of pebble quicklime produced by adding the briquetted lime to the supply of traditional pebble lime.
One problem with the briquetted lime produced to date has been that the crush strength of the briquettes was less than that of natural pebble lime. As a result, the thus formed briquettes would suffer breakage and disintegration during material handling and shipping. Over the years, several additives have been utilized to increase the strength and durability of lime briquettes, including calcium stearate and paper fibers. However, for a multitude of reasons, the production of briquettes using existing additives has not been widely accepted commercially. The use of briquetting additives of the type commonly used for other industrial products is limited for the briquetting of quicklime. This is due not only to the fact that quicklime reacts violently with water, but also because of the potential adverse effect the traditional briquetting additives might have on the end use of the briquetted quicklime.
Over the past several years the US steel industry has utilized increasing amounts of pebble dolomitic quicklime, CaO·MgO, as a fluxing agent. Unfortunately the fine dolomitic quicklime produced during calcining and material handling cannot be used for conventional high calcium quicklime markets.
A need exists, therefore, for an improved method for briquetting dolomitic quicklime which will produce briquettes of sufficient strength to resist the stresses of material handling in both the initial dolomitic quicklime production and also the ultimate end application processing, e.g., the steel customer's handling and processing equipment.
A need also exists for such a briquetting technology in which an improved binder additive is utilized which binder is not detrimental to the end application of the briquettes and may actually be advantageous in such end applications.
A need specifically exists in the steel industry for an improved binder additive for briquetting lime fines which additive has no detrimental effect on the use of the dolomitic quicklime as a steel fluxing agent and which, in the optimum case, actually adds value as the briquette is used in the steel making process.